Spectral analysis of cooling induced hemodynamic perturbations indicates involvement of sympathetic activation and nitric oxide production in rats

Aims Oscillations in arterial pressure and heart period in response to cold stress are poorly understood. We used a telemetric device with spectral and cross-spectral analyses to assess variabilities in the heart rate (HRV) and blood pressure (BPV) of conscious rats receiving a cooling stimulus (CS) (rapid immersion of palms and soles into 4 °C water) at ambient thermoneutral conditions (TC), in a cold room (CC), and when under pentobarbital anesthesia (UA). Main methods Power spectra of very low, low, and high frequencies (VLF: 0.02 to 0.2 Hz, LF: 0.2 to 0.6 Hz, and HF: 0.6 to 3.0 Hz), dicrotic notch (Dn) and plasma nitric oxide (NO) levels were measured for statistical comparisons. Key findings When compared to resting rats (PreCS), CS evoked in rats the following hemodynamic perturbations: 1) pressor and tachycardia; 2) increases in VLF_BPV, LF_BPV, HF_BPV, and TP_BPV but decreases in VLF_HRV, LF_HRV, and TP_HRV; 3) a positive correlation between LF_BPV and VLF_BPV but an inverse correlation between VLF_HRV and VLF_BPV and LF_HRV and LF_BPV; 4) high coherence value at frequency region of LF between BPV and HRV; and 5) increase of NO production and disappearance of Dn. Additionally, CS of CC and UA rats compared with TC rats evoked different patterns of hemodynamic perturbations; CC rats were activated but UA rats were inactivated. Significance Our findings indicate that changes in VLF_BPV are related to the myogenic vascular responsiveness to CS. Power spectra changes to CS are highly relevant to sympathetic activation and NO production.